This invention relates to a rotary-type drum sand classifier which can efficiently produce classified sand which is substantially free of water.
In general, the type of sand classifier which the present invention refers to comprises;
(a) a horizontal rotary drum which has a supernatant water outlet at the front end and a sand outlet at the rear end,
(b) a plurality of helicoid blades for transferring the settled sand which are secured to the inner surface of the rotary drum along the length of the rotary drum, and
(c) a sand discharging means for discharging the above settled sand from the rear outlet of the drum including a plurality of equidistant sand scooping paddles and a cone-shaped discharge chute located at the center of the above scooping paddles.
In the above construction, when the muddy water containing sand is charged into the rotary drum, sand of a desired size distribution is discharged from the rear outlet of the drum while the supernatant water is discharged from the front inlet of the drum.
The applicant of this invention also has disclosed the above type of sand classifier in U.S. Patent Application Ser. No. 759,968 (the C.I.P. of U.S. Patent Application Ser. No. 592,963) which is of great practical merit.
However, referring to the above classifier as shown in FIGS. 7, 8 and 11, at the settled sand discharge end of the drum body a, a plurality of water-separation or scooping paddles b, each of which has a multiplicity of apertures formed therein is radially secured to the inner periphery of the drum 1 in an axial direction. Therefore, the portion or point where the discharge end of the helicoid blade d and the scooping paddle b meet form a considerably acute angle. This implies that the settled sand e which is transferred to the settled sand discharge end by a plurality of helicoid blades tends to accumulate at the deflected or bent portions forming a "dam" between the accumulated settled sand e and the ring-like weir plate f. Therefore, when the paddles provided with those dams are raised upward corresponding to the rotation of the rotary drum, the water defined in the dam is also raised upward. Although a multiplicity of apertures are formed in each scooping paddle, they can not separate the water satisfactorily due to the restriction on the size and number of apertures, therefore the discharged sand still contains a considerable amount of water. Usually, thus produced sand is not directly used as material to produce concrete or construction material since the muddy component contained in the classified sand will ill-affect the rigidity and strength of the construction materials.
Of course, if the thus produced sand is further subject to a water cleaning operation, the muddy component adhering to the classified sand will be removed so that muddy-component-free sand may be produced. Such cleaning operation, however, increases the cost of classification while making the entire classifying operation cumbersome.
Accordingly, it is an object of the present invention to provide a wet-type rotary sand classifier which can resolve the afore-mentioned problems afflicting the conventional apparatuses.
It is another object of the present invention to provide a wet-type rotary sand classifier which can produce a classified sand of improved quality by efficiently separating out the water without necessitating the above cleaning operation.
It is still another object of the present invention to provide a wet-type rotary sand classifier which can conduct the classifying and cleaning operations simultaneously corresponding to the quantity of mud components relative to the muddy water.
It is a further object of the present invention to provide a wet-type rotary sand classifier which has a plurality of apertured helicoid blades for facilitating the rotation of the rotary drum without decreasing the efficiency of the sand transferring operation.
It is a still further object of the present invention to provide a wet-type rotary sand classifier which has a mechanism for preventing the muddy water to influence the settled sand so as to ensure the smooth transfer of the settled sand.